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Report No.

Inprovement of an automatic in situ stress measurement probe and it's application in the field test

Kato, Harumi*

The overcoring tests in the vertical borehole 02SE-04 (a standard HQ-WL) were made at depths of 122.7m, 142.7m, 157.0m, 173.5m and 192.0m by using modified equipments and an automatic probe developed by Japan Nuclear Cycle Development Institute (JNC). By adopting a newly developed wire line type probe carrier and pilot hole drilling tool, it was ensured that quick accomplishment of steps followed during overcoring at great depth was possible. Modifications to a glue capsule were carried out to achieve successful grouting of the SI cell in the pilot hole at great depths. Since cracks developed along the planes of weakness during the overcoring, none of the tests at the five depths provided valid measurement. In order to determine the elastic properties of the overcore and epoxy cement, cyclic loading test was made. The test reviled that the core taken down to a depth of 160m possessed plastic property. It was also found that long periods of up to three days were required for the epoxy cement extruded in the pilot hole to change into elastic material. Hydraulic fracturing tests were also conducted in the borehole 02SE-04 at depths ranging from 125.8m to 168.0m. At two depths, fractures parallel to the borehole axis were induced. The test results indicated that the stress regime at the two depths was reverse faulting tectonic environment (Sv$$<$$Sh$$<$$SH+) and the orientation of the hydraulic fracture trace in 02SE-04 was found to give an average azimuth for the maximum horizontal stress SH of N60°E.



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